Manufacture of rubber



Patented Aug. 14, 1934 outrun MANUFACTURE OF RUBBER Edward Arthur Murphy Erdington, Birmingham,

England, assignor to Dunlop Rubber Company, Limited, Erdington, Birmingham, England, a

British corporation No Drawing. Application December 15, 1933, Serial No. 702,563. In Great Britain November.

4 Claims.

1 592,437, filed February 11, 1932, and Serial No.

610,496, filed May 10, 1932. The main modification or development consists in the step of converting the products obtained after removing all or most of the aqueous medium into a powder.

According to my invention, the process for the production of powder-like compositions containing rubber from aqueous dispersions of rubber or the like of the kinds hereinafter specified comprises efiecting coagulation of the aqueous dispersions aforesaid in' any of the manners set forth in the above applications, removing all or most of the aqueous medium so as to obtain a substantially dry product and converting or crumbling the dried product into a powder.

If desired, the aqueous medium can be removed by a filtration operation followed by a drying operation.

The powder-like compositions produced according to the present invention can be very etficiently used in the production of moulded ing to the present invention can be admixed-with granular, fibrous or divided materials such as leather fibre, wood flour, cork dust, jute fibre, cotton flock, paper pulp, naturally short cellulose fibres and ground fibres or alternatively or additionally with mineral powders such as whiting or sand, eitherby admixing these materials direct with the powder-like compositions or by admixing these additional materials with the intermediate fiocculent or granular precipitates and thereafter removing all or most of the aqueous mediumand converting or crumbling the'substantially dried product into a powder. These powders are also capable of being pressed up cold .to give hard moulded products.

invention are ofp articular use for moulding operations in view of the shortness of the mould cycle and the ability to use bright colours. The ability to produce coherent masses merely by cold moulding appears to be associated with a characteristic The products obtained according to the present adhesiveness frequently observed in connection 1 with fiocculent or granular precipitates.

The method of effecting coagulation of the aqueous dispersions aforesaid in the presence of a relatively large quantity of water as set forth in application Serial No. 592,437 by precipitating in situ one or more compounding ingredients preferably in relatively large proportions on the rubber content by the interaction or double decomposition of one or more water soluble.reagents having normally no coagulating effects upon the aforesaid dispersions with one or more water soluble reagents subsequently added thereto is of particular use in connection with. the present invention.

Examples of the water soluble reagents of the first class having normally no coagulating efiects upon the dispersions are-carbonates, sulphates, silicates of the alkali metals or of ammonium.

Examples of the water soluble reagents of the second class which interact with the water soluble reagents of the first class to produce insoluble compounding ingredients are soluble salts of magnesium, aluminium, calcium, barium or zinc; sodium silicate also falls into. this class if the corresponding reagent in the first class is such as to precipitate silicic acid-e. g. ammonium carbonate. I

By a suitable choice of the reagents and consequent reaction products precipitates of varying consistency can be formed. v g

If desired, the granular precipitates can be washed free from soluble reaction productssuch as soluble sulphates or chlorides by known means such as filtration and washing prior to their y consolidation or concentration. 1 p 1 Numerous substances are capable of being used as compounding ingredients, for example, carbonates of magnesium, calcium and zinc may be prepared from sodium carbonate and sulphates or chlorides of these metals. Similarly the silicates of magnesium and zinc can be prepared from sodium silicate and the corresponding sulphate or chloride.

Mixtures of precipitates may be prepared and Other examples of suitable .coagulants are acetic acid, salts such as zinc sulphate and magnesium sulphate. The emulsions or dispersions of rubber or the like comprise those consisting of rubber, guttapercha, balata or similar vegetable resins occurring naturally or artificially obtained. Such 'artificial aqueous dispersions may include those of coagulated rubber, vulcanized rubber, synthetic rubber, waste or reclaim. If desired,. any of .the aforementioneddisper- 1 sions may be usedalone or in admixture with one another. Any of the aforesaid dispersions may contain the usual known compounding and vulcanizing ingredients and/or may be in concentrated form. v 7

Concentrates such as are obtained in Patent 1,846,164, February 23, 1932, or in British Patent 219,635 to whichjmay beadded any one or more of the usual compounding ingredients may also pe used. u u The aforesaid vulcanizing and other compounding ingredients which are added in the form of their dispersions maybe added to the aforesaid aqueous emulsions or dispersions of rubber or the like prior or subsequent to the precipitation of the granular dispersions.

It is preferable to add the aforesaid dispersions ofithe vulcanizing and other compounding ingredients before the precipitationof the granular dispersions.-

p In; some cases, where the precipitate obtained is found tobe in adamp powdery or short pastelike condition before consolidation into the compact uniform mass; consolidation can be hastened and facilitated by treating the filter cake obtained with a rubber solvent which maybe mixed with a mutual solvent for the water and the rub ber solvent employed, as for instance alcohol.

The following examples illustrate how the process can be effected.

Ewcmple 1 An unvulcanized rubber powder having for example the following suitable composition I 5; 1 Parts by weight Rubber 1 60 Aluminium silicate can-be produced as follovvs 100-parts of concentrated latex of 60%[concentration produced by centrifugalization is diluted to a 5%. concentration; 104 parts of sodium silicate intheform of a 5% solution are stirred into the latex and this isvfollowed by the addition of 96' parts of aluminium sulphate also in the form of a 5% solution. The precipitate so formed is filtered, dried and disintegrated into a powder.

The rubber powderso produced can be formed into a sheet by pressing it up ina cold mould.

, If-desired, the dry uncompounded rubber powder can be mixed with compounding ingredients to form a composition for direct moulding purposes.

Example 2 The flocculent precipitate produced in accordance with Example 1 can be mixed with granite chippings, the admixture allowed to dry and then coarsely disintegrated. The coated chippings may be consolidated into a more or less uniform sheet by cold pressure such as rolling producing in this way rubber products for surfacing roads and other structures.

' I Example 3 A flocculent granular precipitate of the following composition--- 7 Parts by weight Rubber 100 Sulphur 5 Zinc oxide 5 Accelerator 0.5 Aluminium silicate 15 is first prepared as follows To 340 partsby Weight of a rubber latex obtained by centrifugal action, the following. ingredients are added with constant stirring and in the following order In this way, a rubber precipitate is obtained wherein the concentration of the precipitate in the aqueousmedium is 5%.

The resulting rubber precipitate is allowed to drain on a filterand a paste-like mass is obtained containing approximately 18% total solids.

This paste-like mass is compounded with disintegrated leather dust in the proportion to give parts of leather dust to 30 parts of dry precipitate. The admixture is then dried and finally disintegrated.

The disintegrated powder-like crumb canbe put into a mouldand pressed up coldfor 30-40 seconds under a pressure of 5000 lbs., per square inch to produce a hard leather-like moulded article.

Example 4 The paste-like mass prepared according to EX- ample 3 can be mixed with sand and slate flour in the proportion of 10 parts of, rubber precipitate, calculated on the dry weight, 60 parts sand. and 30 parts slate flour. This admixture is dried'and disintegrated.

This powder can be cold moulded under pressure to give a hard wood-like product. Using suit. able compounding ingredients highly coloured horn-like materials can be made in this-way.

Whereas heretofore the flocculent precipitates when dry have been consolidated only by the use of heat and pressure, the present invention proioo iio

vides a powdered rubber compositon with suffiare involved and also makes the moulding operation much easier and simpler.

Having now particularly described my invention, I claim- 1. A method for the manufacture of cold moldable powders comprising rubber material which comprises forming a washable crumb-like suspension of said material from an aqueous dispersion thereof by adding to said dispersion a water soluble reagent having normally no coagulative effect upon the dispersion, then adding a reagent to form a water insoluble, inert, inorganic, compounding ingredient by interaction with said first reagent and simultaneously coagulating said rubber dispersion to form a granular precipitate, drying said precipitate, and disintegrating the same to a powder.

2. The process of claim 1 in which said inorganic inert precipitate is a silicate.

3. The process of claim 1 in which said precipitates are admixed with fillers.

4. A method for the manufacture of cold molded articles comprising rubber material which comprises forming a washable crumb-like suspension of said material from an aqueous disper sion thereof by adding to said dispersion a water soluble reagent having normally no coagulative effect upon the dispersion, then adding a reagent to form a water insoluble inert inorganic compounding ingredient by interaction with said first reagent and simultaneously coagulating said rubber dispersion to form a granular precipitate, drying said precipitate, disintegrating the same to a powder, and compressing said powder without heating to a compact adherent mass.

EDWARD ARTHUR MURPHY. 

